X-ray tube



magma Dec. 28 1926.

M. MORRISON X-RAY TUBE Filed June 16. 1921 INVENTOR MONTFORDNQERIsQN. ATTORNEY Patented Dec. 2 8, 1926.

UNHTED srarns MONTFORD MORRISON, OF NEW YORK, N. Y.

X-RAY TUBE.

Application filed June 16, 192i. Serial No. 477,898.

This invention relates to improvements in electron tubes and more especiully'to such tubes operated for the purpose of producing Roentgen or X-rays.

An object of the invention is the PlOVlSlOIl of an electron tube in which electrons are produced independent of thermionic emission.

Another object of the invention is the provision of a cathode, composite in nature, and circuit arran 'ement therefor, whereby electrons are withc rawn from a cold portion of the cathode.

Another object is the provision of an electron tube free from luminous bodies.

A further object of the present invention is the provision of an electron tube having a commercially long life.

A still further object of my invention is the provision of an X-ray device in which the source of the X-rays need not be electri cally connected to a high voltage circuit.

Other objects will be apparent from the following specification.

In the present state of the art of generating Roentgen or X-rays, it is necessary to cause electrons, to bombard a target at a velocity sufiiciently high to cause X-rays to emanate therefrom. The necessary electrons have been derived in prior devices either from a small quantity of ionizable gas contained' in the tube or from an element operated to emit electrons thermally.

X-ray tubes containing gas are inferior to high vacuum tubes for certain classes of X-ray work: they generate, for example, softer rays, that is to say, rays of lower penetrability than those generated by high vacuum tubes.

Tubes which derive the necessary electrons from a thermally electron-emitting cathode have a limited life because of the very high temperature at which the cathode must be maintained.

My resent invention difi'ers radically from tu es of the prior art, although it may be a high-vacuum device, which might of course, contain a slight amount of residual gas. I have found that it is not necessary to employ an incandescent body as a source of electrons for the generation of X-rays and that they may be withdrawn from a cathode operating at room temperature or a temperature below incandescence, if a suficiently high potential gradient exists in the tube.

The ordinary construction of X-ray tubes can not be used in applying the principle of my invention inasmuch as the necessary potential gradient can not be generated in such tubes. However, by means of a special construction I am enabled to secure a sufliciently high potential gradient and a field sufficient- 1y intense to withdraw electrons from a comparatively coldcathode when employing voltages of a practicable value.

c It is obvious that the maintenance of the cathode at a non-luminous temperature gives to it and therefore to the tube as a whole, an indefinitely long life, whereas a cathode operating at incandescence is naturally limited in life due to evaporation.

In addition to utilizing, for the generation of X-rays, the primary electrons which are extracted from a cold cathode my device makes use of secondary electrons which are generated by the impact of a portion of the primary electrons on a solid metallic element. It is known that for every electron which collides with a metal, a large number of sec- 3 ondary electrons are emitted therefrom. The utilization of this phenomenon is an advantage in that a second source of electrons is provided.

As another novel and useful feature, my

invention makes possible a tube in which the body acting as the source of X-rays need not be connected to a source of high-potential as in tubes of the prior art, although it may be so connected if desired. The advantage of having the source of X-rays free from high potential lies in the fact that an intense electrostatic field, with the consequent liability to puncture the envelope, is thereby avoided.

An embodiment of my invention comprises a cathode of any desired form operating at a temperature below which electrons may be thermally emitted therefrom, high potential means for withdrawing primary electrons from the comparatively cold cathodev and adapted to emit secondary electrons when the primary electrons impinge thereon and a body' disposed in the path of the electron stream adapted to emanate X-rays when electrons impinge thereon.

My invention will be best understood by reference to the following description taken in connection with the accompanying drawings in which,

Figure 1 is an elevational view, partly in siecion, of one form of my improved tube; an

Figure 2' is a view of a modified form of the high potential element relatively positioned with respect to the anti-cathode.

Referring to Figure 1, showing one embodiment of my invention, an envelope is indicated at 3 consisting of any suitable matcria-l such as glass. Into the tubular end 4- of the envelope 3 is sealed a target 5 which functions as the source of X-rays and consists of a material of high atomic weight, such, for example, as tungsten. Although any suitable form .may be given the target 5, it is here shown as a truncated cylinder beveled at 7 to eliminate the thin edge resulting from truncation. A lead wire 8 is shown in position to variably connect the target 5 electrically to a sour ce of high potential 16. However, I may choose to leave the target 5 electrically free from such a source of potential. I

Opposite the target 5 is a dished metallic plate 9, constituting the cathode of the tube, adapted to be self-focusing by reason of its form and positioned to present its concave surface to the target 5. The cathode 9 is provided with an electrically conducting lead wire 10 which is sealed into the tubular end 12 of envelope 3 by means of stem Li 5 mally therefrom.

Interposedbetween cathode 9 and target 5 in very close proximity to the cathode 9 is a conducting element 20 supported in any practical manner, and sealed into the enenvelope 3. The element 20 is variably connected by means of a conductor 24, sealed through the envelope at 22, to a source of high potential 16 and is preferably of a metallic nature consisting for example of a material such as aluminum.

of a pointed needle, sharp edge or element of very small radius of curvature, or plurality of the same in order to secure an electric field suflicientlyintense to enable electrons to be withdrawn from cathode 9.

When a high potential is impressed between cathode 9 and element 20 the former being negatbvely and the latter positively charged, electrons are withdrawn from the comparatively cold cathode 9. To permit the free passage of a portion of these electrons the element 20 is preferably provided with perforations or apertures like a grid and the electrons passing through these perforations are focused to impinge on the focal spot 25 of target 5 whereupon X-rays emanate from'the latter body.

A fraction of that portion of primary electrons which collide with element 20 have sufficient velocity to cause secondary elec- The structure of the element 20 preferably takes the form eraeer trons to be emitted from the latter element. Part of these secondary electrons are focused to impinge on the target and cause to be connected as usual to a souice of high potential and are of course enclosed within an evacuated envelope. In accordance with Fig. 2, the electrode 20 constitutes the cathode from which electrons may be withdrawn to impinge on the anodeb, at high velocity, to generate X-rays.

In radiographic work it isobviously necessary to exclude'light from the plate on which the image falls. In employing tubes of the prior art which required an incandescent element as a source of electrons it was necessary to provide means to prevent light from such source from falling on the image plate. My tube avoids this difficulty by not haxzing any luminous elements therein.

While the preferred embodiment of the invention has been illustrated, it will be understood'that many structural changes may be effected therein and it is, therefore, de-

sired to be understood that the invention is to be limited only by the scope of the appended claims.

l/Vhat is claimed is:

1. In an X-ra device of the high-vacuum 2. In a high-vacuum electron tube, a cathode and perforated means at high potential, in close proximity thereto, whereby it is adapted to have electrons withdrawn therefrom. v

3. In an X-ray device, the combination of a cathode operating at a temperature below that which electrons may be emitted thermall therefrom and a perforated element at high potential comprising portions of a very small radii of curvature in close proximity thereto, for withdrawing electrons therefrom.

4. In an X-ray device, perforated highpotential means closely positioned with respect to and adapted'to withdraw electrons from a cathode operating at a temperature below which electrons may be emitted thermally therefrom.

5. In an X-ray device, a self-focusing cathode and perforated means comprising sharp portions for drawing electrons therefrom bv eslablishinga high-potentialgradlent therebet ween. and a target separate from said means.

(i. In an X-ray device, a target, a cathode a and a high potential element separatefrom I said target and positioned in close proxima cooperal ing cathode operable at a temperature below which electrons may be emitted thermally therefrom, perlorated means mterposed between said target and said cathode lin close proximity to said cathode for \vitl'idrawing elections therefrom. v

9. In an X-raydevice, the con'lbination of a target,-a source of electrons operating at a temperature ,below which electrons may be emitted thermally therefrom and perforated means at high potential for extracting electrons from said source.

I target.

10. In an X-ray device, the combination of a target, 'a source of electrons operating at a temperature below which electrons may be emitted thermally therefrom and a sharp high-potential element in close proximity thereto. 1

11. In an X-ray device, the combination of a cathode electrically connected to a source of high potential, a source of X-rays electrically free from the source of high 0- tential and a high-potential element isposed in close proximity to said cathode.

12. In an X-ray devlce, the combination of a target, a cathode operating at a temperature below which electronsmay be emitted thermally therefrom and a high potential pointed grid through which primary electrons are emitted by said cathode to said 13. In an X-ray device, the combination of a target, a cathode operating at a temperature below which electrons may be emitted thermally therefrom and a high potential element operating to extract electrons from said cathode, closely positioned thereto and disposed in the path of a ortion of the electrons emitted from sai cathode sc'con'dar electrons when primary electrons collidet iorewith. I

14. In an X-ray device, the combination of a target, a cathode emitting'primary elecwhereby' said element becomes the source of I trons at a tem rature below,v which they.

may betherma y. emitted therefrom and a closely spaced element at high potential and emittm secondary electrons at a temperature be ow which electrons may be thermally emitted therefrom.

1 5. The combination with a source of high potential, of an X-ray device com rising a sealed envelope, :1. target, a cold out rods and an intermediateelement electrically connected to the source of high potential, and disposed in close roximity to said cathode for withdrawin o ectrons therefrom.

16. An -ray device comprising a sealed envelope, an anode, 'a cooperating cathode, said cathode operable ata temperature below which electrons may be emitted thermally therefrom and means at high potential for extracting electrons from said cathode.

17. An X-ray' device comprising an evacuated sealed envelope, a target therein adapted to emanate X-rays, a cooperating cathode operating at a temperature below which electrons may be emitted thermally therefrom and means connected to a source of high potential interposed between said anode and said cathode in close proximity to said cathode for extracting the electrons,

therefrom.

18. The method of generating X-rays comprising withdrawing electrons from a body at a temperature below that at which electrons ma be emitted thermally .therefrom by esta lishing a high-potential gradient near a source of electrons, to cause electrons to impinge on another body spaced farther off.

The method of generating X-rays WhlCh consists in connecting to a source of high potential an electrode which functions at a temperature below which electrons may be emitted thermally therefrom, withdrawing electrons from said electrode by means of a high-potential element comprising sharp portions disposed in close proximity thereto and causing said electrons to impinge on a source of X-rays.-

In testimony whereof, I have hereunto subscribed my name this fifteenth day of June 1921.

MONTFORD MORRISON. 

